1. Field of the Invention
The present invention relates generally to efficient coupling of laser beams into multimode waveguides and specifically to waveguide lasers and amplifiers based on low phonon energy glasses or crystals doped with external or impurity atoms or ions, and more particularly to devices using waveguides based on such glasses that incorporate high concentration of atoms or ions.
2. Description of the Prior Art
Because of the strong water absorption near 3 xcexcm in tissue and the consequent ultrashort penetration depths (of a few microns), compact high power (100 mW to 1 W) 2.7 xcexcm laser sources with TEM00 beam quality have several important applications in ultrafine intraocular and endoscopic laser surgery including transmyocardial revascularization and other intra-arterial procedures. Compact and efficient sources of mid-IR radiation are also needed for infrared countermeasures applications, and for ppb (parts per billion)level spectroscopic monitoring of several important species such as carbon monoxide (CO), formaldehyde (H2CO), nitric oxide (NO), nitrogen dioxide (NO2), hydrogen sulfide (H2S), arsine (AsH3), and phosphine (PH3).
The 2.7 xcexcm transition in Er:ZBLAN is well-suited for several of the above applications. For instance, the broad tunability of this transition (2.65-2.83 xcexcm) should enable ppb spectra monitoring of H2S (2.65 xcexcm) and NO (2.7 xcexcm). However, as has been frequently stated, the longer natural lifetime of the lower laser level (4I13/2, 9.4 ms) relative to that of the upper laser level (4I11/2, 7.5 ms) of the 2.7 xcexcm transition often results in a population bottleneck that inhibits efficient steady-state (CW) lasing in Er:ZBLAN fiber lasers. As such this transition has been frequently called xe2x80x9cself-terminatingxe2x80x9d.
Efficient coupling of radiation from diode arrays into multimode waveguides and in particular, to the inner cladding, multimode waveguide, of a double clad fiber is a key issue in the realization of high power diode-pumped fiber lasers. Specifically, it is often necessary to correct for any astigmatism in the diode beam in order to couple into the inner cladding efficiently. In addition, the beam shape of the diode radiation has to match the shape of the inner cladding, e.g. circular, rectangular, etc. Currently, such astigmatism correction and beam shaping are typically performed by a prism pair or by the use of two or more lenses. Beam shaping has also been performed using either an aperture or parallel stacked plates or a multimode fiber.
It is therefore an object of the present invention to provide an improved highly doped fiber laser and/or amplifier that will provide high efficiency and high power output.
It is a further object to provide a highly doped fiber laser and/or amplifier which greatly reduces or eliminates the bottleneck associated with the longer lifetime of the lower laser level 4I13/2 if Er is used as a dopant.
It is yet another object to provide a fiber laser and/or amplifier that has a dopant at a concentration level that results in clusters of such dopants.
It is yet another object to provide highly doped fiber laser and/or amplifier having a dopant that greatly enhances cross-relaxation.
It is yet another object to provide highly doped fiber laser and/or amplifier having a dopant that greatly enhances cross-relaxation by creating ion or dopant clusters.
It is yet another object to provide sensitizer ions or atoms to assist in the depopulation of lower energy levels through the energy transfer process.
In all of the above embodiments, it is an object to provide a highly doped fiber laser and/or amplifier that has a dopant concentrations between 1,001 and 149,999 ppm.
It is an object of the present invention to provide a method for efficient coupling of light from an optical source or an array into a multimode waveguide.
It is yet another object of the present invention to provide a method for astigmatism correction in a laser that may be performed by a single optical element.
It is yet another object of the present invention to provide a method for beamshaping of a laser with a single optical element.
According to a first broad aspect of the present invention, there is provided a highly doped waveguide comprising: a waveguide; a dopant consisting of Er disposed in the waveguide; and sensitizer ions consisting of Pr disposed in the waveguide, wherein the dopant has a concentration of between 1,000 to 150,000, wherein the sensitizer ions have a concentration of between 100 and 20,000 ppm, and wherein the concentration of the dopant enhances cross-relaxation between two elements of the dopant.
According to a second broad aspect of the present invention there is provided a highly doped optical material comprising: a low phonon energy bulk material; a dopant consisting of Er disposed in the bulk material; and sensitizer ions consisting of Pr disposed in the bulk material, wherein the dopant has a concentration of between 1000 and 150,000 ppm, the sensitizer ions have a concentration between about 100 and about 20,000 ppm, wherein the waveguide contains clusters of the dopant, and wherein the clusters enhance cross-relaxation between two elements of the dopant.
According to a third broad aspect of the present invention there is provided a highly doped bulk material laser comprising: a low phonon energy bulk material; a dopant consisting of Er disposed in the bulk material; sensitizer ions consisting of Pr disposed in the bulk material; a resonant cavity, the resonant cavity being defined by a first and second reflective means at an amplification wavelength and disposed at two ends of the bulk material; and an energy source for injecting energy into the bulk material, wherein the dopant has a concentration of between 1,000 and 150,000 ppm, the sensitizer ions have a concentration between about 100 and about 20,000 ppm, and wherein the dopant enhances cross-relaxation between two elements of the dopant.
According to a fourth broad aspect of the present invention there is provided a highly doped bulk material amplifier comprising: a low phonon energy bulk material; a dopant consisting of Er disposed in the bulk material; sensitizer ions consisting of Pr disposed in the bulk material; and an energy source for injecting energy into the bulk material, wherein the dopant has a concentration of between 1,000 and 150,000 ppm, the senitizer ions have a concentration between about 100 and about 20,000 ppm, and wherein the dopant enhances cross-relaxation between two elements of the dopant.
According to a fifth broad aspect of the present invention there is provided a device for coupling an optical source to a multimode waveguide, the device comprising: an optical source, the optical source having an optical plane associated therewith; a waveguide; and a coupling means comprising an optical element, the optical element having a light receiving surface, a lens axis and an optical element axis, the optical element being rotated around the optical element axis to create an angle of rotation between the lens axis and the optical plane.
According to a sixth broad aspect of the present invention there is provided a device for coupling an optical source to a waveguide, the device comprising: an optical source, the optical source having an optical plane associated therewith; a waveguide; and an astigmatism correction and beam shaping means, the means comprising a single optical element, the optical element having a light receiving surface, a lens axis and an optical element axis, the optical element being rotated around the optical element axis to create an angle of rotation between the lens axis and the optical plane.
According to a seventh broad aspect of the present invention there is provided a high power diode-pumped fiber laser, the fiber laser comprising: an array of diode lasers, the array of diode lasers having an optical plane associated therewith; a waveguide; and an astigmatism correction and beam shaping means, the means comprising a single optical element, the optical element having a light receiving surface, a lens axis and an optical element axis, the optical element being rotated around the optical element axis to create an angle of rotation between the lens axis and the optical plane.
According to an eighth broad aspect of the present invention there is provided a device for coupling an optical source to a waveguide, the device comprising: a waveguide; a dopant consisting of Er disposed in the waveguide; sensitizer ions consisting of Pr disposed in the waveguide, wherein the dopant has a concentration of between 1,000 to 150,000, wherein the sensitizer ions have a concentration of between 100 and 20,000 ppm, and wherein the concentration of the dopant enhances cross-relaxation between two elements of the dopant; an optical source, the optical source having an optical plane associated therewith; and a coupling means comprising an optical element, the optical element having a light receiving surface, a lens axis and an optical element axis, the optical element being rotated around the optical element axis to create an angle of rotation between the lens axis and the optical plane.
Other objects and features of the present invention will be apparent from the following detailed description of the preferred embodiment.